A data path often includes devices known as selectors and cross-connectors so that connections between a variety of inputs and a variety of outputs can be configured electronically. Such devices are known generally as digital selection circuits and may, for example, selectively connect one of 16 inputs to one of 16 outputs. Should such a device fail such that an incorrect input is connected to a given output, the fault would often be undetected. Many applications include information that can be periodically extracted to determine whether the correct payload is being carried. However, in some applications, it is not possible to extract such information from the payload. In these latter applications then, the ability to ensure that a point where a misconnection may occur is monitored to detect such a failure is desirable. As a consequence of failing to detect a connection fault, incorrect traffic may be connected on the given output to downstream equipment. Further, the traffic cannot be guaranteed, nor can the fault be isolated when detected by some means external to the transmission.
U.S. patent application Ser. No. 09/397,968 provides a method and apparatus for ensuring that connection failures occurring in a data path will be detected. This allows the fault to be isolated, protected and alarmed, thus avoiding improper traffic routing and facilitating subsequent repair. In accordance with one aspect of the application, there is provided a method of monitoring a connection unit, the connection unit comprising a primary connection map for receiving connection control signals and a primary connection circuit for receiving input from the primary connection map and for performing primary connections between a plurality of inputs and a plurality of primary outputs, the primary connections based on the connection control-signals, the method including receiving the connection control signals and the plurality of inputs. The method further includes performing secondary connections between the plurality of inputs and a plurality of secondary outputs, the secondary connections based on the connection control signals, receiving the plurality of primary outputs and determining a connection integrity status indicator from the plurality of primary outputs and the plurality of secondary outputs. In another aspect of the application a connection integrity monitor is provided for carrying out this method.
Unfortunately, the connection integrity monitor of the referenced application requires complete replication of the primary connection circuit which is very inefficient in terms of power, gate usage and cost.